The principal area of focus for this project is the identification of heritable characteristics of ion transport which may distinguish individuals with a primary affective disorder from normal controls. The lithium plasma/erythrocyte ratio has been examined along with other parameters as possible predictors of lithium response during depression. High platelet monoamine oxidase and "augmentation" of visual average evoked response were found to be the best predictors. Lithium plasma erythrocyte ratio was not found to be a good predictor. A study of sodium potassium stimulated adenosine triphosphatase (Na ion-K ion ATPase), a cation transport enzyme, is beginning. An assay is being developed to determine the level of this membrane enzyme in bipolar and unipolar depressed patients and in normal controls. A twin study will serve to determine heritability of this enzyme.